1. Field of the Invention
This invention relates to a plasma display panel (hereinafter, referred to as “PDP”), and more particularly, relates to a PDP in which barrier ribs of a closed type that divide a discharge space into respective cells are disposed between a pair of substrates forming a panel.
2. Description of the Related Art
An AC drive three-electrode face discharge type PDP has been known as a conventional PDP. This PDP is manufactured by aligning a front-side substrate on which desired constituent elements such as electrodes, dielectric layers, phosphor layers and barrier ribs are formed and a back-side substrate face to face with each other and by sealing the peripheral portion thereof.
The sealing process of the front-side substrate and the back-side substrate is carried out through the following processes: a glass sealing material containing low-melting point glass is applied to the peripheral portion of the substrates and the glass sealing material is fused and anchored by heat so that the substrates are bonded to each other. In this bonding process, a vacuum-exhausting process is carried out on the inside of the panel through a vent pipe formed on the back face side of the back-side substrate so that impurity gases are removed and an inert gas such as Ne and Xe is then sealed in the panel as a discharge gas.
In this PDP, barrier ribs are formed through the following processes: a paste-form material for the barrier ribs, made from glass frit, a binder resin and a solvent, is applied to a substrate and dried thereon so that a material layer for barrier ribs is formed, and the material layer for barrier ribs is patterned to form a pattern layer for barrier ribs is formed, and by firing the pattern layer for barrier ribs, the barrier ribs are formed.
As the structure of the barrier ribs, the following structures are employed: a linear barrier-rib structure (referred to as a stripe rib structure) in which a discharge space is separated only in the row direction by forming a plurality of barrier ribs in the column direction, and a closed-type barrier-rib structure (referred to as a box rib structure, a waffle rib structure, a mesh rib structure, etc.) in which the discharge space is divided into respective cells by forming barrier ribs in the row direction and barrier ribs in the column direction (see Japanese Unexamined Patent Publication No. Hei 11-213896). In recent years, in order to improve the display brightness and achieve pixels with high precision, there have been strong demands for PDPs having the closed-type barrier-rib structure.
As described above, in the manufacturing process of the PDP, impurity gases need to be removed from the inside of the panel by carrying out a vacuum exhausting operation through a vent pipe. In this case, the PDP having the closed-type structure of barrier ribs has a smaller ventilation conductance in the panel in comparison with the PDP having the linear structure of barrier ribs, resulting in difficulty in exhausting the impurity gases. When the removal of the impurity gases is insufficient, the characteristics of the panel deteriorate. More specifically, there is a reduction in the brightness and variations in the voltage due to degradation of the phosphor, and display irregularities in the panel tend to be caused.
For this reason, with respect to the PDP having the closed-type structure of barrier ribs, various structures for barrier ribs, used for improving the vent (exhaust) path inside the panel, have been proposed. For example, in the case of a PDP having a rectangular cell structure formed by dividing the discharge space by barrier ribs in the row direction and barrier ribs in the column direction, a structure has been known in which each barrier rib in the row direction is divided into two portions in the column direction, a groove formed in the divided portion is used as a vent passage so that this vent passage is utilized as a vent path when bonding the front-side substrate and the back-side substrate to each other so as to be sealed.
In the case of this barrier-rib structure with a vent passage, since, upon firing the barrier ribs, the barrier ribs in the column direction shrink due to thermal shrinkage at the time of the firing process, the barrier ribs in the row direction tilt toward the cell side, resulting in a narrowed cell area. For this reason, the aperture ratio (area of cell region/area of display region) becomes smaller, resulting in a problem of low display brightness. Here, a phosphor paste is applied to the inside of each cell, and by firing the phosphor paste, the phosphor layer is formed; however, the reduction in the aperture ratio tends to impair the stability in the phosphor paste applying process.